VH-4S issue - burnt some caps?

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reussen

reussen

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Hey all,

At a gig yesterday, I experienced my first ever issue with a VH-4S! :confused:

I was only using one side of the amp; I'm waiting for a new cab! Of course, the side I wasn't using was turned down to zero.. Hope that's not what caused the issue! Playing on CH3, I noticed my volume was dropping significantly. Switching to CH4 for leads brought it back up. Power tubes seemed ok; all lighting up and looking good.

I figure it must be something tube-related, though... Any thoughts?

Thanks!

Robert
 
Normally a tube amp must be having a speaker load, even if it's turned to 0, unless there are individual standby switches for each side, then I think you could leave one on standby (I did with my 2502 poweramp).

Could be you blew something.

But from the description you gave, it seems more like a preamp tube went pushing the daisies.
 
Thanks for that.. I'll look at the pre-amp tubes! Anyone else have an idea?
 
reussen":urayuioa said:
Hey all,

At a gig yesterday, I experienced my first ever issue with a VH-4S! :confused:

I was only using one side of the amp; I'm waiting for a new cab! Of course, the side I wasn't using was turned down to zero.. Hope that's not what caused the issue! Playing on CH3, I noticed my volume was dropping significantly. Switching to CH4 for leads brought it back up. Power tubes seemed ok; all lighting up and looking good.

I figure it must be something tube-related, though... Any thoughts?

Thanks!

Robert
Click to expand...

Always run a load on both sides... :gethim:
 
Hmm... I tried the VH-4S yesterday for the first time after the sunday night gig. Things are not looking good. Going from stand-by to run gave me a nasty humm (Masters both @ zero); not coming from the speakers, but from the VH-4S. Playing through ANY of the 4 channels gives me extra notes; sounds like a detuner with tremolo effect. Power tubes seem fine; nothing visibly noticeable, but I haven't changed them. Checked and replaced pre-amp tubes, but no change.

I guess something's blown, but I have no idea where to start looking. I probably did this to myself; hooking up only 1 load and playing the gig. :doh:

If anyone has a suggestion, please let me know.

-Robert
 
am i correct that the output transformer can be blown by not applying a load?

you can buy a load resistor for about 5€, solder some jack to it and use it as a replacement for a speaker on the side of the poweramp you're not using. something like this :

http://www1.conrad.de/scripts/wgate/zco ... chedetail=

(sorry, it's in german)

or...... you solder your cabinet to be stereo...
 
Some extra info on this problem (I was there ;) ):

- outputs 'hum' 50Hz on both channels, even with volume all the way down
(well, it's more than a hum)
- when playing through either channel, sounds like a tremolo-effect with added octave below

Didn't try to send the output of the pre-amp to another poweramp and the other way round to exclude either pre- or poweramp, but we will do that on saturday :aww:

My best guesses for now by only listening:

- busted poweramp-tubes (strange, that all 4 go at the same time) - don't think it's the output transformer as both sides act the same.
- some error in the (HV / glow) supply (because the hum is there even when all volumes are down), either a busted (bridge)rectifier/cap

Anyone know where I should look at first (I'm probably the one who's gonna do the measuring)
Scope/DVM etc. are all available.

Hope to know more after testing poweramp and preamps separately

All hints are appreciated!
 
Hmm, looky what I found when opening her up...

P1000866.JPG


P1000867.JPG


Can't remember that goo being there when I opened her up last time for biasing.

Peter (or any other tech guru) - could this cap hidden beneath the goo be responsible for the humming sound?

Looks like its connected to the big rectifier in the front (can't even see clearly because of the goo...

Where can I get another one? ;)
 
A few minutes soldering later:

P1000870.JPG


Anyone got some caps? ;)

Do you all think I will be okay replacing these two? I'll check if the rectifier isn't broken also.

Could these caps have taken anything else 'with' them?
 
Got the caps on their way, let's see how it sounds when these are replaced.

If it still isn't right, I think I'll send it to my local tube-guitar-guru. I know my electronics, but without a schematic tube-amps are not my thing ;)

Will keep you posted,

Hans
 
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